1. Field of the Invention
The present invention relates to a bent-axis machine that includes a housing having a control cover and a piston drum, rotatably mounted in the housing on a valve plate, having axial cylinders, of which each cylinder accepts a piston, having a drive flange allocated to a drive shaft, on which flange the free ends of the pistons protruding from the cylinders are supported, and having an adjustment system including a pivot cradle for adjusting the displacement volume, having an actuating drive with which the piston drum with the valve plate can be pivoted by a maximum operating range relative to the drive axis, the range being limited by a minimum and a maximum angle of rotation, and a hydraulic fluid guiding via the pivot cradle taking place through the valve plate.
2. Discussion of the Related Art
Bent-axis machines in the sense of the present invention are hydraulic machines that, as axial piston pumps, are used to convert mechanical energy, i.e. torque or rotational speed, into hydraulic energy, i.e. volume flow or pressure, or, as axial piston motors, are used to convert hydraulic energy (volume flow or pressure) into mechanical energy (torque or rotational speed). Bent-axis machines of this type are known for example from EP 0 728 945 A1 and from EP 0 409 084 A2. Bent-axis machines are standardly fashioned in such a way that the piston drum in the control cover (the housing head) can be pivoted, with an actuating drive, between a minimum pivot angle of approximately 0° and a maximum pivot angle of up to 32 or 33°, this region being fashioned as a pivot cradle. The supplying of the piston pump, namely the intake duct and the pressure duct, are here guided via, or through, the stated pivot cradle. The range by which the piston drum can be pivoted between the minimum and maximum pivot angle in the housing is limited by the design, and is determined in particular by the control plate (valve plate) guided in the pivot cradle in the control cover, which, when the minimum pivot angle is fallen below, or when the maximum pivot angle is exceeded, no longer allows a properly functioning supply and carrying off of hydraulic fluid through the control cover. In particular, when these limits are exceeded hydraulic fluid escapes from the flow channels between the control cover and valve plate into the housing, so that the reliable functioning of the machine is no longer ensured.
As long as a pivot angle of 0° is set, i.e. the drive shaft axis and the piston drum axis coincide, the bent-axis machine does not convey any volume flow; that is, in this operating state the machine has practically no displacement volume. If the piston drum with the pistons is pivoted in the direction of the maximum pivot angle, i.e. the pistons are pivoted out to the side, then during the rotational movement the pistons, triggered by the oblique positioning of the piston drum on the inner side of the bend, move deeper into the cylinder, and on the outer side of the bend move out of the cylinder in the direction of bottom dead center. When there is a rotation, the pistons are alternately pulled out of the cylinder, or pressed into the cylinder, through the connection with the drive flange. In this way, when the pistons are pulled away from the control plate there arises a partial vacuum in the cylinders that suctions the hydraulic fluid into the cylinder via the pivot cradle. On the other side, when the pistons are displaced toward the control plate there arises an excess pressure that drives hydraulic fluid out of the cylinder and out of the hydraulic aggregate via the pivot cradle.
Such bent-axis machines can be mass-produced relatively inexpensively. However, as already mentioned, the maximum range of adjustment is limited by the design. If, as a result of conditions of use, a larger range of adjustment is to be covered or is required, then bent-axis machines having yoke adjustment must be used, i.e. hydraulic aggregates that permit a range of adjustment of from 0° to 45°. In these machines, whose design requires a large outlay and which are therefore very expensive, the housing is divided into two or more parts, and the housing casing, enclosing the piston drum, is capable of being pivoted relative to the housing part that accommodates the drive shaft. Precisely this design requires significant additional design outlay and monetary expense, and for this reason bent-axis machines having yoke adjustment are not available for traction drives in the low-cost segment.
US 2006/0110265 A1 discloses a swash plate machine that is used in particular as a pump unit for high-pressure cleaners. The stated swash plate machine relates only to a conveyor pump that functions purely passively, in which the conveying pressure is set automatically as a function of the conveyed volume, via passive elements, in particular elastomer elements.